JP7567026B2 - Separator for electrochemical device and method for manufacturing same - Google Patents

Description

This application claims priority based on Korean Patent Application No. 10-2020-0120881, filed September 18, 2020.

The present invention relates to a separator for an electrochemical device and a method for manufacturing the same, and more particularly to a separator for an electrochemical device that contains inorganic particles and has improved adhesion to an electrode, and a method for manufacturing the same.

Recently, lithium-ion secondary batteries have been widely used as power sources for portable electronic devices such as notebook computers, mobile phones, digital cameras, and camcorders. These lithium-ion secondary batteries are also used in transportation such as electric vehicles due to their high energy density.

As portable electronic devices become smaller and lighter, the exterior packaging of non-aqueous secondary batteries is becoming simpler. Initially, stainless steel battery cans were used as the exterior packaging, but then aluminum can packaging was developed, and currently soft-pack packaging made of aluminum laminate packs has also been developed. In the case of soft-pack packaging made of aluminum laminate, the packaging is flexible, so there is a technical issue that gaps may form between the electrodes and the separator during charging and discharging, resulting in poor cycle life. From the perspective of solving this issue, technology for bonding the electrodes and the separator is important, and many technical proposals have been made.

Typically, a separator for an electrochemical device has a structure including a porous polymer film (separator substrate) and an inorganic coating layer formed on at least one surface of the separator substrate. The inorganic coating layer includes inorganic particles and a binder polymer, and is introduced for the durability (prevention of membrane breakage, etc.) and heat resistance (prevention of thermal shrinkage, etc.) of the separator substrate. PVdF (Polyvinylidene fluoride)-based resins are mainly used as the binder polymer for such separators, and an adhesive surface layer with a high binder resin content is formed near the surface of the inorganic coating layer by migrating the binder resin to the separator surface through a humidified phase separation method. However, the adhesive strength of the PVdF-based resin itself is not high, making it difficult to ensure a high level of binding strength. To improve the adhesive strength, the content of the binder polymer or the amount of coating can be increased, but this undesirably increases the thickness of the adhesive layer, lowers the energy density, and increases the resistance. The adhesive layer of the separator must be able to provide both high adhesive strength and high ionic conductivity even with a thin thickness, and in order to stably use the battery for a long period of time, the separator must be made of a chemically and electrochemically stable material, and the manufacturing process for the separator must be highly productive and allow for mass production at low cost. As a result, there is a growing demand for the development of a separator for secondary batteries that satisfies the above requirements.

The present invention aims to provide a separator including an inorganic coating layer that has improved adhesion to an electrode. Another object of the present invention is to provide a method for producing a separator having the above characteristics. It is easily understood that other objects and advantages of the present invention can be realized by the means or methods described in the claims and combinations thereof.

The first aspect of the present invention relates to a separator for an electrochemical device, the separator comprising a porous polymer film substrate and an inorganic coating layer formed on at least one surface of the substrate, the inorganic coating layer comprising inorganic particles and a binder polymer, the inorganic particles comprising composite particles in which at least a portion of the surface of the inorganic particles is coated with a coupling compound, the coupling compound has a functional group introduced therein capable of binding the inorganic particles to the binder resin, the functional group comprising at least one selected from an alkyl group, an alkoxy group, and an ester group, and the binder polymer comprises an amorphous polymer and/or a partially crystalline polymer having a glass transition temperature (Tg) of 60° C. or less.

A second aspect of the present invention is the first aspect, wherein the binder polymer includes one or more compounds represented by the following chemical formula 1:
In Formula 1, R is each independently -H, -OR ₄ , -C(=O)-R ₄ , -C(=O)O-R ₄ , -OC(=O)-R ₄ or -C(=O)NH-R ₄ , and R ₄ is each independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group, m is an integer of 1 or more, and n is 0 or an integer of 1 or more.

The third aspect of the present invention is the second aspect, in which the binder polymer includes at least one selected from polyvinyl acetate (PVAc) and ethylene-vinyl acetate copolymer (polyethylene-co-vinyl acetate).

The fourth aspect of the present invention is any one of the first to third aspects, in which the binder polymer has a weight average molecular weight (Mw) of 600,000 or less.

The fifth aspect of the present invention is any one of the first to fourth aspects, wherein the coupling compound includes a silane-based compound and/or a titanate-based compound.

The sixth aspect of the present invention is any one of the first to fifth aspects, wherein the inorganic coating layer contains the inorganic particles at a ratio of 50% by weight or more relative to 100% by weight of the total amount of the binder polymer and the inorganic particles, and has a porous structure due to interstitial volumes between the inorganic particles.

The seventh aspect of the present invention is any one of the first to sixth aspects, in which the inorganic coating layer includes an electrode adhesive portion in which the binder polymer is distributed at a higher concentration in the surface layer portion than in other portions.

The eighth aspect of the present invention is any one of the first to seventh aspects, wherein the binder polymer further includes a crystalline binder resin.

The ninth aspect of the present invention is a method for manufacturing a separator according to any one of the first to eighth aspects, the method including the steps of: preparing a polymer solution by adding a solvent and a binder polymer; preparing a slurry for forming an inorganic coating layer by adding inorganic particles to the polymer solution; and coating the slurry on a surface of a porous polymer film substrate and drying the substrate under humid conditions to perform a humid phase separation process; an electrode adhesive portion having a high content of binder resin is formed on the surface of the inorganic coating layer by the humid phase separation process.

The tenth aspect of the present invention is the ninth aspect, in which the inorganic particles include composite particles coated with a coupling compound.

The separator according to the present invention includes a partially crystalline and/or amorphous polymer such as PVAc and EVA as a binder polymer in the inorganic coating layer, and the surfaces of the inorganic particles are coated with a coupling agent to prevent the inorganic particles from being detached from the inorganic coating layer. In addition, when the separator is manufactured, phase separation is promoted under humid conditions, and an adhesive part in which a large amount of the binder polymer is distributed on the surface of the separator is provided, improving the binding strength with the electrode.

The drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the above-described content of the invention, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to only the matters shown in such drawings. Meanwhile, the shape, size, scale, and ratio of elements in the drawings included in this specification are exaggerated to emphasize a clearer description.

1 is a schematic diagram illustrating a cross-sectional structure of a separation membrane according to an embodiment of the present invention. 1 is a graph showing the results of IR measurement of Composite Particle 1 of an example. 1 is an image showing the surface of a separation membrane obtained through Example 1 of the present invention. 1 is an image showing the surface of a separator obtained in Comparative Example 9 of the present invention.

The present invention will be described in detail below. Prior to this, the terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that correspond to the technical ideas of the present invention, based on the principle that an inventor can appropriately define the concepts of terms in order to best describe his/her invention. Therefore, it should be understood that the configurations shown in the embodiments and drawings described in this specification are merely the most preferable embodiment of the present invention, and do not represent the technical ideas of the present invention, and therefore, at the time of this application, there are various equivalents and modifications that can replace them.

Throughout the specification of this application, when a part "includes" a certain component, this does not mean to exclude other components, but means that it may further include other components, unless specifically stated to the contrary.

In addition, the terms "about," "substantially," and the like, used throughout the specification of this application, when manufacturing and material tolerances inherent in the referred meaning are presented, are used to mean a numerical value or close to a numerical value, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute numerical values are referred to in order to facilitate understanding of this application.

Throughout the specification of this application, the statement "A and/or B" means "A or B or all of these."

Certain terminology used in the detailed description of the connected inventions is for convenience only and is not limiting. The words "right", "left", "top" and "bottom" designate directions in the drawings to which reference is made. The words "inwardly" and "outwardly" designate directions toward or away from the geometric center of the designated device, system or component thereof, respectively. "Front", "back", "upper", "lower" and related words and phrases designate locations and orientations in the drawings to which reference is made and are not intended to be limiting. Such terms include the words enumerated above, derivatives thereof and words of similar import.

In this specification, content ratios are based on weight unless otherwise specified.

The present invention relates to a separator for an electrochemical device and a method for manufacturing the same. In the present invention, the electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a concept that includes a primary battery and a secondary battery. The secondary battery is capable of being charged and discharged, and is a concept that includes lithium ion batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc.

1. Separation Membrane 1) Structure of Separation Membrane The separation membrane 100 according to the present invention includes a porous polymer substrate 110 and an inorganic coating layer 120 formed on at least one surface of the porous polymer substrate 110. The inorganic coating layer includes inorganic particles and a binder polymer.

In the present invention, the binder polymer includes an amorphous and/or partially crystalline polymer. In addition, in the present invention, at least a part or all of the surface of the inorganic particles is coated with a coupling compound. In addition, the inorganic coating layer may have a porous structure due to the space (interstitial volume) between the inorganic particles. In addition, in one embodiment of the present invention, the inorganic coating layer has an adhesive part having a predetermined thickness and a high content of the binder polymer in the surface layer, which provides a high binding strength with the electrode.

In one embodiment of the present invention, the separation membrane has a thickness of 5 to 30 μm, and is appropriately adjusted within this range. For example, it is 10 μm or more or 25 μm or less. In addition, the separation membrane has an air permeability in the range of about 50 to 3000 sec/100 cc.

The term "permeability" as used herein means the time it takes for 100 cc of air to pass through an object to be measured for permeability, such as a separation membrane or a porous polymer substrate, and may be expressed in units of seconds/100 cc. It may be used interchangeably with permeability, and is usually expressed as a Gurley value. In a specific embodiment of the present invention, the permeability is measured in accordance with JIS P8117.

Meanwhile, in the present invention, the porosity and pore size are measured using an adsorption gas such as nitrogen using a BELSORP (BET equipment) manufactured by BEL JAPAN Co., Ltd., or by a method such as mercury intrusion porosimetry or capillary flow porosimetry. Alternatively, in one embodiment of the present invention, the thickness and weight of the obtained inorganic coating layer can be measured, and the porosity can be calculated from the measured thickness and weight and the theoretical density of the inorganic coating layer.

The porous polymer substrate refers to a substrate having a plurality of pores formed therein and a porous ion-conducting barrier that allows ions to pass while blocking electrical contact between the negative electrode and the positive electrode. The pores are interconnected to each other, allowing gas or liquid to pass from one side of the substrate to the other side.

The material constituting such a porous polymer substrate can be any organic or inorganic material having electrical insulation properties. In particular, from the viewpoint of imparting a shutdown function to the substrate, it is desirable to use a thermoplastic resin as the constituent material of the substrate. Here, the shutdown function refers to the function of blocking the movement of ions and preventing thermal runaway of the battery when the battery temperature becomes high by dissolving the thermoplastic resin and closing the holes in the porous substrate. As the thermoplastic resin, a thermoplastic resin with a melting point of less than 200°C is appropriate, and polyolefin is particularly desirable.

In addition, the porous polymer substrate may further include at least one of polymer resins such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. The porous polymer substrate may be, but is not limited to, a nonwoven fabric, a porous polymer film, or a laminate of two or more of these.

Specifically, the porous polymer substrate is any one of a) to e) below.

a) a porous film formed by melting/extruding a polymer resin;
b) a multilayer film in which two or more of the porous films of a) are laminated;
c) a nonwoven web produced by accumulating filaments obtained by melt/spinning a polymer resin;
d) a multilayer film having two or more layers of the nonwoven fabric web of b) laminated thereon;
e) A porous composite membrane having a multi-layer structure comprising two or more of the above a) to d).

In the present invention, the porous polymer substrate preferably has a thickness of 3 to 12 μm or 5 to 12 μm. If the thickness is less than this range, the conductive barrier function is insufficient, while if the thickness is too much above this range (i.e., too thick), the resistance of the separator increases excessively.

In one embodiment of the present invention, the weight average molecular weight of the polyolefin is desirably 100,000 (g/mol) to 5,000,000. If the weight average molecular weight is less than 100,000, it may be difficult to ensure sufficient mechanical properties. If it is greater than 5,000,000, the shutdown characteristics may deteriorate or molding may become difficult.

In the present specification, the term molecular weight refers to weight average molecular weight (Mw). The unit may be g/mol. Such molecular weight may be measured, for example, using gel permeation chromatography (GPC, PL GPC220, Agilent Technologies).

The puncture strength of the porous polymer substrate is 300 gf or more from the viewpoint of improving the production yield. The puncture strength of the porous substrate refers to the maximum puncture load (gf) measured by a puncture test using a Kato tech KES-G5 handy compression tester under the conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm/sec.

In a specific embodiment of the present invention, the porous polymer substrate can be any planar porous polymer substrate used in electrochemical devices. For example, an insulating thin film having high ion permeability and mechanical strength, a pore diameter of typically 10 to 100 nm, and a thickness of typically 5 to 12 μm is used.

3) Inorganic Coating Layer In the present invention, the separator includes an inorganic coating layer formed on at least one surface of the porous polymer substrate. The inorganic coating layer includes a mixture including a binder polymer and inorganic particles. The inorganic coating layer is attached to each other by a binder (i.e., the binder polymer connects and fixes the inorganic particles) so that the inorganic particles can be kept bound to each other inside the layer. In one embodiment, the inorganic particles are packed in a dense state and may have a number of micropores due to interstitial volumes formed between the inorganic particles. These micropores are connected to each other to form a porous structure that allows gas or liquid to pass from one side to the other side. In one embodiment of the present invention, the inorganic particles are coated on all or at least a part of the surface with a binder polymer, and the particles are bound to each other by the binder polymer through surface and/or point bonding. In one embodiment of the present invention, the inorganic particles are included in the inorganic coating layer at a ratio of 50% by weight or more, preferably 60% by weight or more, 70% by weight or more, or 80% by weight or more, based on 100% by weight of the total amount of the binder polymer and the inorganic particles, and more preferably 95% by weight or less, or 90% by weight or less, within the above range.

The inorganic coating layer preferably has a thickness of 1 to 5 μm on one side of the porous polymer substrate. The thickness can be preferably 3 μm or more, and within this range, the adhesive strength with the electrode is excellent, resulting in increased cell strength of the battery. On the other hand, if the thickness is 4 μm or less, it is advantageous in terms of the cycle characteristics and resistance characteristics of the battery.

Meanwhile, in the present invention, the inorganic coating layer has an electrode adhesive portion 121 having a high content of binder polymer in the surface portion due to the characteristics of the manufacturing method described below. FIG. 1 is a schematic diagram of a cross-sectional structure of a separator 100 according to an embodiment of the present invention. Referring to this figure, the separator of the present invention has an inorganic coating layer 120 formed on the surface of a porous polymer substrate 110, and the binder polymer is distributed at a higher concentration in the surface portion of the inorganic coating layer than in other portions. In this specification, for convenience of explanation, the surface portion where the binder polymer is distributed at a higher concentration is referred to as the "electrode adhesive portion 121". In one embodiment of the present invention, the electrode adhesive portion is a result of the binder polymer migrating to the surface portion by a manufacturing method such as humid phase separation. Therefore, the electrode adhesive portion is not a structure physically separated from the inorganic coating layer, but is inseparably bonded to the surface of the inorganic coating layer as a part of the inorganic coating layer, and the thickness of the electrode adhesive portion is non-uniform.

B. Materials of Inorganic Coating Layer B1. Binder Polymer In one embodiment of the present invention, the binder polymer includes a semi-crystalline polymer, an amorphous-crystalline polymer, or a mixture thereof. In one embodiment of the present invention, in consideration of improving the adhesive strength between the electrode and the separator, the semi-crystalline polymer has a crystallinity of 60% or less. Specifically, the binder polymer may include one or more compounds represented by the following Chemical Formula 1:

In Formula 1, R is each independently -H, -OR ₄ , -C(=O)-R ₄ , -C(=O)O-R ₄ , -OC(=O)-R ₄ or -C(=O)NH-R _4. In addition, R ₄ is each independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group. m is an integer of 1 or more, and n is an integer of 0 or 1 or more. In one embodiment of the present invention, the compound of Formula 1 may include at least one selected from polyvinyl acetate (PVAc) and ethylene vinyl acetate copolymer.

In one embodiment of the present invention, the crystallinity is expressed as a percentage by dividing the melting enthalpy (ΔH) value measured by DSC by the melting enthalpy (ΔH) value of a theoretically perfect crystal (crystallinity 100%). Here, the melting enthalpy value of a theoretically perfect crystal can be found in the Polymer Handbook for known polymers, and for unknown or newly synthesized materials, it can be calculated by extrapolation, which involves extending the crystallinity of two or more points.

In one embodiment of the present invention, the binder polymer has a glass transition temperature of 60°C or less, preferably 30 to 50°C. When the binder polymer satisfies this range, the adhesive strength between the separator and the electrode is improved, for example, an electrode-separator adhesive strength of 300gf/25mm (60°C, 6.5MPa) or more can be secured. In the present invention, the adhesive strength is based on the result of dissolving the binder polymer in acetone at a concentration of 5wt%, coating it on a polymer film substrate at 23°C and 45% relative humidity, and adhering the obtained result to an electrode at 60°C and 6.5MPa, and measuring the peel strength.

Meanwhile, in one embodiment of the present invention, the binder polymer preferably has a weight average molecular weight (Mw) of 600,000 or less. If the molecular weight (Mw) exceeds this range, it is difficult to ensure sufficient electrode adhesion.

In the present specification, the term molecular weight refers to weight average molecular weight (Mw). The unit may be g/mol. Such molecular weight may be measured, for example, using gel permeation chromatography (GPC, PL GPC220, Agilent Technologies).

Meanwhile, in one embodiment of the present invention, the binder polymer may further include a fluorine-based binder polymer such as polyvinylidene fluoride, polyvinylidene fluoride hexafluoroethylene, polyvinylidene fluoride trifluoroethylene (TrFE), polyvinylidene fluoride chlorofluoroethylene (CTFE), polyvinylidene fluoride 1,2-difluoroethylene, or polyvinylidene fluoride tetrafluoroethylene (TFE). In addition, polymethylmethacrylate, polybutylacrylate, polybutylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, acetylpropionyl cellulose, etc. propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxymethyl cellulose. Such additional binder polymers may be one or more of the above examples. The content of the additional binder polymer is appropriately adjusted in consideration of the adhesive strength, and is, for example, in the range of 30 wt% or less with respect to 100 wt% of the binder polymer.

In addition, in one embodiment of the present invention, the inorganic coating layer may further include additives such as a dispersant and/or a thickener in the range of 1 to 3 wt % based on 100 wt % of the inorganic coating layer. In one embodiment of the present invention, the additive may be one or more of polyvinylpyrolidone (PVP), polyvinylalcohol (PVA), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethylhydroxyethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, and cyanoethyl polyvinyl alcohol.

B2. Inorganic Particles In a specific embodiment of the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and/or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li/Li+). In particular, when inorganic particles having a high dielectric constant are used as the inorganic particles, they can contribute to an increase in the degree of dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

For the reasons described above, it is preferable that the inorganic particles include high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or greater include _BaTiO3 , Pb(Zr,Ti) _O3 (PZT), Pb1 _{- xLaxZr1} - _yTiyO3 (PLZT, 0<x<1 _{, 0} < _y <1), Pb( _Mg1/3Nb2 / ₃ ) _O3 - _PbTiO3 ( _PMN -PT), hafnia (HfO2), _SrTiO3 , SnO2, _CeO2 , MgO, _NiO , _CaO , ZnO, ZrO2, _SiO2 , _Y2O3 , _Al2O3 , Al(OH) ₃ , AlOOH, SiC, and _{TiO2 ,} or mixtures thereof _.

As the inorganic particles, inorganic particles having a lithium ion transfer ability, that is, inorganic particles that contain lithium element but do not store lithium but have the function of transferring lithium ions, can be used. Non-limiting examples of inorganic particles having lithium ion transporting ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) _x O _y -based glasses (0<x<4, 0<y<13) such as 14Li ₂ O- ₉ Al ₂ O ₃ -38 TiO ₂ -39 _{P 2} O ₅ ), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0<x<2, 0<y<3), Li _3.25 Ge _0.25 P _0.75 S Examples of such glasses include lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0<x<4, 0<y<1, 0<z<1, 0<w<5) such as lithium germanium thiophosphate ₄ , lithium nitrite (Li _x N _y , 0 _< x<4, 0<y<2) such as Li _{3 N} , SiS ₂ -based glasses (Li _x Si _y S _z , 0<x<3, 0<y<2, 0<z<4) such as Li 3 PO _{4 -Li 2 S} -SiS 2, P 2 S ₅ -based glasses (Li _x P _y S _z , 0<x<3, 0<y<3, 0<z<7) such as LiI-Li ₂ S-P ₂ S _5, or mixtures thereof.

Meanwhile, in one embodiment of the present invention, the inorganic particles may include composite particles whose surfaces are coated with a coupling compound. The composite particles have at least a part or all of their surfaces coated with a coupling compound. In this specification, the coating means that the coupling agent is bonded or attached to the surface of the inorganic particles by a method such as chemical, physical, or electrochemical.

In a specific embodiment of the present invention, the coupling agent has at least one functional group selected from the group consisting of an alkyl group, an alkoxy group, and an ester group, and examples of such coupling agents include silane-based coupling agents, fatty acids, and titanate-based coupling agents, of which one or more are used.

On the other hand, when the coupling agent contains an alkyl group, it is preferable that the number of carbon atoms is 8 or less. When the number of carbon atoms exceeds 8, the dispersibility in ketone-based solvents such as acetone, which has high polarity, is low, which is disadvantageous in the production of a slurry for forming an inorganic coating layer.

The silane coupling agent may contain two or more functional groups selected from the group consisting of a phenyl group, a vinyl group, an epoxy group, an amino group, an acryloxy group, a methacryloxy group, a methoxy group, an ethoxy group, an alkyl group, an isocyanurate group, and an isocyanate group. Examples of such silane coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, ... Examples of the silane include trimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, decyltrimethoxysilane, and trifluoropropyltrimethoxysilane. One or a mixture of two or more of these silanes may be used.

The fatty acids include, for example, stearic acid, palmitic acid, lauric acid, oleic acid, linoleic acid, etc., and one or a mixture of two or more of these may be used.

Examples of the titanate coupling agents include monoalkoxy titanates, neoalkoxy titanates, isopropyl tridioctyl phosphate titanate, isopropyl tridioctyl pyrophosphate titanate, oleyl titanate, isopropyl trioleyl titanate, isopropyl tristearyl titanate, and isopropyl triisostearyl titanate. For example, titanium acylates such as tributoxy titanium stearate, isopropoxy titanium triisostearate, and mono-i-propoxy titanium tri-i-stearate; titanium alkoxides such as titanium tetraethoxide, titanium tetrapropoxide, titanium tetrabutoxide, tetracyclohexyl titanate, and tetrabenzyl titanate; titanium chelates such as di-n-butoxy bis(triethanolaminate) titanium, titanium diisopropoxy bis(acetylacetonate), titanium tetraacetylacetonate, titanium di-2-ethylhexoxy bis(2-ethyl-3-hydroxyhexoxide), and titanium diisopropoxy bis(ethyl acetoacetate); and the like, among which one or a mixture of two or more types may be included.

Meanwhile, the average particle size of the inorganic particles is not particularly limited, but is preferably in the range of 0.1 to 1.5 μm in order to form an inorganic coating layer of uniform thickness and to have an appropriate porosity. If it is less than 0.1 μm, the dispersibility decreases, and if it exceeds 1.5 μm, the thickness of the inorganic coating layer formed increases.

2. Method for Producing Inorganic Coating Layer A method for producing a separation membrane according to one aspect of the present invention includes the steps of preparing a slurry for an inorganic coating layer, the slurry including inorganic particles, a binder polymer, and a solvent; and coating or drying the slurry on at least one surface of a separation membrane substrate. The drying step is performed under humid conditions. Alternatively, the drying step is performed by drying the porous substrate coated with the slurry in a non-solvent for the binder polymer, for example, under humid conditions, so that the binder resin is solidified and migrates to the separation membrane surface.

First, the prepared binder polymer is dissolved in a solvent to prepare a polymer binder solution. Then, the polymer binder solution is added to a mixture containing inorganic particles and a solvent, and mixed to prepare a slurry for forming an inorganic coating layer. The inorganic particles are added in a crushed state to have a predetermined average particle size. Alternatively, the inorganic particles can be added and then crushed and dispersed while controlling the crushing to have a predetermined average particle size using a ball mill method or the like. An auxiliary agent such as a dispersant can be further added to the mixture and/or slurry as necessary.

It is then applied to a porous polymer substrate and left to stand for a specified period of time under humid conditions to solidify (dry) the binder polymer.

Under these humidification conditions, the binder polymer solidifies, inducing phase separation of the binder polymer in the slurry. In one embodiment of the present invention, the humidification conditions are a relative humidity of about 30 to 70%. During this phase separation, the solvent migrates to the surface of the inorganic coating layer, and the binder polymer migrates to the surface of the inorganic coating layer as the solvent migrates, forming an electrode adhesive part with a high binder polymer content on the surface, thereby providing high adhesive strength between the electrode and the separator.

The solvent may be a component capable of dissolving the binder polymer used. It is preferable to use a ketone-based solvent as such a solvent. In one embodiment of the present invention, specific examples of the solvent may be appropriately selected and used from polar amide solvents such as acetone, methyl ethyl ketone, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide, but are not limited thereto.

Meanwhile, as described above, the inorganic particles may include composite particles whose surfaces are coated with a coupling agent. The composite particles may be prepared by a spray coating method in which a solution in which a coupling agent is dispersed is sprayed onto the surfaces of the inorganic particles to coat the surfaces of the inorganic particles with the coupling agent. Alternatively, the inorganic particles may be dispersed in a suitable solvent such as water, and then the coupling agent may be added and stirred to coat the surfaces of the inorganic particles with the coupling agent. The method of coating or covering the inorganic particles with the coupling agent is not limited to any one particular method, and known covering methods such as a spray coating method may be used.

On the other hand, the application of the slurry is not particularly limited, and conventional coating methods such as a Mayer bar, a die coater, a reverse roll coater, and a gravure coater can be applied. When forming the inorganic coating layer on both sides of the separation membrane, it is possible to apply the coating liquid to each side at a time, and then perform humid phase separation and drying. However, from the viewpoint of productivity, it is more preferable to apply the coating liquid to both sides of the porous substrate at the same time, and then perform humid phase separation and drying.

3. Electrode Assembly Including the Separator The present invention provides a secondary battery including the separator. The battery includes an anode, a cathode, and a separator interposed between the anode and the cathode, and the separator has the characteristics described above.

In the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer on at least one surface of the current collector, the positive electrode active material layer including a positive electrode active material, a conductive material, and a binder polymer. The positive electrode active material may be a layered compound such as lithium manganese composite oxide (LiMn ₂ O ₄ , LiMnO _{2 ,} etc.), lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; a lithium manganese oxide such as a compound having a chemical formula Li _x Mn _y Ni _z Co _(1-y-z) O ₂ (x is 0.5 to 2, x + y + z = 1), a compound having a chemical formula Li _{1 + x} Mn _2-x O ₄ (wherein x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , or LiMnO ₂ ; a lithium copper oxide (Li ₂ CuO ₂ ); a lithium copper oxide such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ , or Cu vanadium oxides such as vanadium _oxide ( _VO ) ₇ ; lithium nickel oxides with the formula LiNi _1-x M _x O ₂ (wherein M is one or more selected from Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and x is 0.01 to 0.3); lithium nickel oxides with the formula Li _a Ni _x Co _y Mn _z O ₂ (wherein 0<a<1.5, 0<[x, y, z]<1, x+y+z=1), LiMn _2-x M _x O ₂ (wherein M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 to 0.1), or Li ₂ Mn ₃ MO _8. The lithium manganese complex oxide represented by the formula (wherein M=Fe, Co, Ni, Cu, or Zn); _LiMn2O4 in which part of the Li in the chemical formula is replaced with an alkaline earth metal ion; disulfide compounds; _{and Fe2} ( _MoO4 ) ₃ , which may include one or a mixture of two or more of these.

In the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer on at least one surface of the current collector, the negative electrode active material layer including a negative electrode active material, a conductive material, and a binder polymer. The negative electrode may contain, as a negative electrode active material, a lithium metal oxide, carbon such as non-graphitizable carbon or graphite-based carbon; a metal composite oxide such as Li _x Fe ₂ O ₃ (0<x≦1), Li _x WO ₂ (0<x≦1), or Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogens; 0<x≦1;1≦y≦3;1≦z≦8); lithium metal; a lithium alloy; a silicon-based alloy; a tin-based alloy; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , or Sb ₂ O _{5 .} The conductive material may include one or a mixture of two or more selected from the following: metal oxides such as GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ and Bi ₂ O ₅ ; conductive polymers such as polyacetylene; Li-Co-Ni based materials; and titanium oxide.

In a specific embodiment of the present invention, the conductive material is, for example, any one selected from the group consisting of graphite, carbon black, carbon or metal fibers, metal powder, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials. More specifically, the conductive material is any one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, stainless steel, copper, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc., can be used.

The binder polymer may be any polymer commonly used by those skilled in the art for electrodes. Non-limiting examples of such binder polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, acetylpropionyl cellulose, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxymethyl cellulose, but are not limited thereto.

The electrode assembly prepared as described above can be inserted into a suitable case and electrolyte injected to manufacture a battery.

In the present invention, the electrolyte is a salt having a structure of A ⁺ B ^- , where A ⁺ includes an alkali metal cation such as Li ⁺ , Na ⁺ , or K ⁺ or an ion consisting of a combination thereof, and B ^- includes PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N(CF ₃ SO ₂ ) ₂ - , C(CF ₂ SO ₂ ) ₃ ^- , or a combination thereof. A salt containing an anion such as ^- or an ion consisting of a combination thereof is dissolved or dissociated in an organic solvent including, but not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone (g-butyrolactone), an ester compound, and a mixture of one or more selected from the above.

Meanwhile, in a specific embodiment of the present invention, the organic solvent contains an ester-based compound, and preferably, the ester-based compound is 30% by weight or more, 50% by weight or more, 60% by weight or more, or 65% by weight or more relative to 100% by weight of the organic solvent.

In a specific embodiment of the present invention, the ester compound includes one or more selected from the group consisting of isobutyl propionate, isoamyl propionate, isobutyl butyrate, isopropyl propionate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

The present invention also provides a battery module including a battery including the electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, a power tool powered by a battery-type motor; electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems.

The present invention will be described in detail below with reference to examples. However, the examples according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[Production of separation membrane]
Examples 1 to 6
The composite particles and the binder resin were put into acetone to obtain a slurry for forming an inorganic coating layer. The solid content of each slurry, excluding acetone, was about 13 to 15 wt %. The slurry was applied to both sides of a separator (polyethylene, porosity 45 vol %, thickness 9 μm), and then dried under a relative humidity of 23° C. and 45% humidity. After drying, the thickness of the coating layer was 6 μm on both sides (3 μm on each side), and the loading of the coating layer was 7.2 g/m ² relative to the separator area. Then, it was cut into a size of 60 mm (length)×25 mm (width) to obtain a separator. FIG. 3 shows the surface of the separator obtained according to Example 1 of the present invention, and it can be seen that the binder resin covers the surface of the coating layer due to phase separation of the binder resin. The compositions of the inorganic particles/composite particles and the binder polymer used in each example are the same as those in Table 1 below. In Table 1 below, Examples 1, 3, 5, and 6 used Al(OH) ₃ (D50: 900 nm) surface-treated with trimethoxypropylsilane as the composite particle (Composite Particle 1), and Examples 2 and 4 used Al(OH) ₃ (D50: 900 nm) surface-treated with isopropyltrioleyltitanate as the composite particle (Composite Particle 2). The composite particles were obtained by spraying solutions containing each coupling agent onto the inorganic particle surface while stirring the Al(OH) ₃ particles, and then drying at 90° C. for 2 hours.

Composite particle 1 was subjected to IR analysis to confirm the presence or absence of a surface coating. Figure 2 shows the results of IR analysis of an uncoated composite particle and composite particle 1, which confirmed the C-H peak and Si-O peak that are the result of the coating.

Meanwhile, the presence or absence of coating was confirmed for composite particle 2 through evaluation of dispersibility. Uncoated particles (Al(OH) ₃ ) and PVAc were mixed in a weight ratio of 75:25 and then poured into acetone. The solid content excluding the solvent was 15 wt%. The mixture was placed in a Dispersion Analyzer (Lumisizer, LUM Co.) and rotated at a speed of 1,000 rpm to apply centrifugal force, and the sedimentation rate over time was measured. Meanwhile, a similar experiment was conducted for composite particle 2. The results are summarized in Table 2 below. As can be seen from Table 2 below, it was confirmed that the sedimentation rate of coated composite particle 2 was significantly reduced compared to uncoated particles due to the coating with a titanate-based compound.

Comparative Examples 1 to 8
The inorganic particles, binder resin, and dispersant were added to acetone to obtain a slurry for forming an inorganic coating layer. The solid content of each slurry, excluding acetone, was about 13 to 15 wt%. The slurry was applied to both sides of a separator (polyethylene, porosity 45 vol%, thickness 9 μm), and then dried under a relative humidity of 23° C. and 45% humidity. After drying, the thickness of the coating layer was 6 μm on both sides (3 μm on each side), and the loading of the coating layer was 7.2 g/ ^m2 relative to the separator area. Then, it was cut into a size of 60 mm (length)×25 mm (width) to obtain a separator. The compositions of the inorganic particles/composite particles and binder polymer used in each comparative example are the same as those in Tables 3 and 4 below.

Comparative Example 9
A slurry for forming an inorganic coating layer was obtained in the same manner as in Example 1. The slurry was applied to both sides of a separator (polyethylene, porosity 45 vol%, thickness 9 μm) and then naturally dried at room temperature to remove the solvent. After drying, the thickness of the coating layer was 6 μm on both sides (3 μm on each side), and the loading of the coating layer was 7.2 g/ ^m2 relative to the separator area. FIG. 4 shows the surface of the separator obtained in Comparative Example 9, and no phase separation of the binder resin occurred, and no binder resin was observed on the surface of the inorganic coating layer. As a result, it was more difficult to ensure electrode adhesion than in the examples.

(2) Evaluation Experiment 1) Evaluation of Peeling Force The separators obtained from Example 1 and Comparative Example 5 were cut to a size of 15 mm x 100 mm. A double-sided adhesive tape was attached to a glass plate, and the prepared separator was attached so that the surface of the inorganic coating layer was attached to the adhesive tape. Then, the end of the attached separator was mounted on a UTM device (LLOYD Instrument, LF plus), and a force was applied at a measurement speed of 300 mm/min at an angle of 180° to measure the force required to peel the inorganic coating layer from the porous polymer substrate. In the case of Example 1, the peeling force was measured to be 127 gf/15 mm, and in the case of Comparative Example 5, it was measured to be 36 gf/15 mm. Thus, it was confirmed that the separator according to the present invention has excellent peeling force when PVDF-HFP, which is a crystalline polymer, is used.

2) Evaluation of Electrode Adhesion The adhesion between the electrode and the separator was measured. First, artificial graphite (average particle size 16 μm), Super C65, styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 95.9:1:1.9:1.2, respectively, and water was added to prepare a negative electrode slurry. The negative electrode slurry was applied to a copper foil in a thickness of 65 μm, and vacuum dried and rolled at about 130° C. for 8 hours to prepare a negative electrode of 1.4875 cm ^2. At this time, the loading of the negative electrode was prepared to be 3.60 mAh/cm ² .

The obtained negative electrode was cut to a size of 25 mm x 100 mm. Separators prepared in Examples (1 to 6) and Comparative Examples (1 to 8) were also cut to a size of 25 mm x 100 mm. The prepared separator and negative electrode were stacked on top of each other, inserted between 100 μm PET films, and then bonded using a flat press. In this case, the flat press conditions were heating and pressing at 60 ° C and a pressure of 6.5 MPa for 1 second. The bonded separator and negative electrode were attached to a slide glass using double-sided tape. The end of the separator adhesive surface (10 mm or less from the end of the adhesive surface) was removed and attached to a 25 mm x 100 mm PET film and single-sided adhesive tape so that the longitudinal direction was connected. Then, the slide glass was attached to the lower holder of the UTM equipment (LLOYD Instrument, LF plus), and the separator and the attached PET film were attached to the upper holder of the UTM equipment. A force was applied at 180° at a measurement speed of 300 mm/min to measure the force required to peel off the inorganic coating layer facing the anode and cathode. In the cases of Examples 1 to 6, the measured adhesive strength exceeded 100 gf/25 mm, but Comparative Examples 1 to 8 showed adhesive strength values that were much lower than this.

Claims (8)

A separator for electrochemical devices,
The separator includes a porous polymer film substrate and an inorganic coating layer formed on at least one surface of the substrate.
The inorganic coating layer includes inorganic particles and a binder polymer,
The inorganic particles include composite particles in which at least a portion of the surface of the inorganic particles is coated with a coupling compound,
The coupling compound has a functional group capable of binding the inorganic particles and the binder polymer , and the functional group includes at least one selected from an alkyl group, an alkoxy group, and an ester group;
The binder polymer includes an amorphous polymer and/or a partially crystalline polymer having a glass transition temperature (Tg) of 60° C. or less,
The binder polymer is at least one compound represented by the following formula 1:
The binder polymer includes at least one compound represented by the following Chemical Formula 1 and a crystalline binder polymer, and the crystalline binder polymer is included in an amount of 30% by weight or less based on 100% by weight of the binder polymer,
Here, R is each independently -H, -OR ₄ , -C(=O)-R ₄ , -C(=O)O-R ₄ , -OC(=O)-R ₄ or -C(=O)NH-R ₄ , each R ₄ is independently hydrogen or a substituted or unsubstituted C1 to C5 alkyl group, m is an integer of 1 or more, and n is 0 or an integer of 1 or more;
Separation membrane for electrochemical elements. 2. The separator for an electrochemical device according to claim 1 , wherein the binder polymer comprises at least one selected from the group consisting of polyvinyl acetate (PVAc) and ethylene-vinyl acetate copolymer. 3. The separator for an electrochemical device according to claim 1, wherein the binder polymer has a weight average molecular weight (Mw) of 600,000 or less. The separator for an electrochemical device according to claim 1 , wherein the coupling compound comprises a silane-based compound and/or a titanate-based compound. 5. The separator for electrochemical devices according to claim 1 , wherein the inorganic coating layer contains the inorganic particles in a ratio of 50% by weight or more with respect to 100% by weight of a total amount of the binder polymer and the inorganic particles, and has a porous structure due to interstitial volumes between the inorganic particles. The separator for an electrochemical device according to claim 1 , wherein the inorganic coating layer includes an electrode adhesive portion in which the binder polymer is distributed at a higher concentration in a surface layer portion than in other portions. A method for producing the separation membrane according to any one of claims 1 to 6 ,
The method comprises:
preparing a polymer solution by adding a solvent and a binder polymer;
preparing a slurry for forming an inorganic coating layer by adding inorganic particles to the polymer solution;
and applying the slurry to a surface of a porous polymer film substrate and drying the slurry under humid conditions to perform a humid phase separation process.
The humid phase separation process forms an electrode adhesive portion having a high content of binder polymer on the surface of the inorganic coating layer. The method for manufacturing a separator for an electrochemical device according to claim 7 , wherein the inorganic particles include composite particles coated with a coupling compound.

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